Impact of two sequential super typhoons on coral reef communities in Palau

Abstract

Typhoons generally develop in the warm tropics, but rarely damage coral reefs between the latitudes 10°N and 10°S because they intensify at higher latitudes. However, climate change is forcing anomalous weather patterns, and is causing typhoons to take less predictable trajectories. For the first time in 70 yr, in December 2012, a super typhoon passed near the island of Palau, located at 7°N in the western tropical Pacific Ocean. A year later, another super typhoon passed over the northern reefs of Palau. This study characterized the impacts of both typhoons on coral and fish assemblages in 3 habitats (i.e. outer reefs, patch reefs, and inner reefs) and at 2 depths (i.e. 3 and 10 m). Loss of coral cover was highest on the shallow, eastern slopes (~60% coral cover). Juvenile coral densities decreased along the western reef slope and on the inner reefs, where overall coral cover scarcely decreased. These results suggested a potential stockrecruitment relationship with corals on the damaged eastern reefs. Early successional corals, particularly pocilloporids, recruited 6 mo after the second typhoon. Fish communities were generally un altered by the first typhoon, except small parrotfishes, which doubled in density along the eastern reef-slope and increased on the inner reefs following the second typhoon. In combination, these findings demonstrate high spatial variability in coral loss, overall decreases in juvenile corals, and increases in herbivorous fishes on a tropical reef system that has rarely experienced large typhoon waves.

Sensitivity of coral recruitment to subtle shifts in early community succession

“…The typhoons severely reduced coral cover along the eastern barrier reef and significantly reduced juvenile coral abundances (Gouezo et al. ). Immediately following the first typhoon, a bloom of the red foliose macroalga Liagora lasted for 9 months at reefs with moderate to high wave exposure (Roff et al.…”

Drivers of recovery and reassembly of coral reef communities

“…Black bars represent degree heating weeks (DHW) in 1 July -30 Sept 1998, 2010 and 2014 [40]. Black lines in the eastern outer reef habitat represent two typhoons occurrence (December 2012 and November 2013, [29] Merulinidae SEM showed a poor fit as IGR was not affected by any variable (electronic supplementary material, figure S6). However, juvenile coral density was positively affected by the availability of substrate, which was higher on the outer reefs and at 3 m across all habitats.…”

“…Throughout the Palau archipelago, nearly 50% of the live corals were totally bleached by the 1998 El-Niñ o mass coral bleaching event [27], and by 2001 more than 80% of 315 reefs around Palau only had 0-5% Acropora cover [28]. Palauan reefs then experienced 14 years without any major disturbance, until two category-5 (Simpson scale) typhoons inflicted an average 60% loss in live coral cover along its eastern outer reefs in 2012 and 2013 [29]. Between these major disturbances, there was a minor thermal stress event in 2010 that induced little mortality [30].…”

Reduced carbon emissions and fishing pressure are both necessary for equatorial coral reefs to keep up with rising seas

“…Ocean acidification will increase chemical‐reef erosion of carbonate framework (Doney et al ). Increasing cyclone intensity and shifts in cyclone trajectories will impact the rates of physical‐reef erosion (Gouezo et al ). Increases in human‐population densities, local pollution (Risk et al ) and fishing pressure (Carreiro‐Silva and McClanahan ) will increase biological‐reef erosion.…”